SendKeys cannot run inside this application

Question

I am reading data from the serial-port in one window application which is already build by Bill Acceptor Company. Now i want to read the value from that application to my window application. I am using Sender.send key for this and it is working fine when i click on button event but i want to use timer and when i use this, I get an Exception in my .NET application saying "SendKeys cannot run inside this application because the application is not handling Windows messages".

Any help?

Vijay Yadav · Answer

Hi Sam Thanks a lot. I agree with you. But the thing is that I ma not able to do this even with WM_SETText and WM_GETTEXT. I hope you have understood my requirement clearly. Please help me and meanwhile i will start the new thread.

Sam Hobbs · Answer

WM_COPY and WM_PASTE will not do anything that WM_GETTEXT and WM_SETTEXT cannot do. So if you are trying to use WM_COPY and WM_PASTE instead of WM_GETTEXT and WM_SETTEXT then you should use WM_GETTEXT and WM_SETTEXT. If however you are askinghow to use WM_COPY and WM_PASTE to solve a different problem then you need to create a separate thread for that. Since this thread has gotten so long it is better to create a new thread for this discussion also. In your new thread you need to explain the details of the requirements for your program; not the programming details of how to do it but the requirements of what the program needs to do. In other words it is my understanding that you need to execute another program wait for the program to start communications then get text from a textbox. I think we do not have enough of the details like that of what you need.

Vijay Yadav · Answer

Ya Sam i know it is for copying and pasting but i want o know how to implement it.

Sam Hobbs · Answer

Well you certainly are reading the documentation. WM_COPY is for copying a textbox's contents to the clipboard and WM_PASTE is for putting text into a textbox from the clipboard'.

Vijay Yadav · Answer

Hi still not done. I have gone thtrough the document and i tried to do but unsucessful. As i don't know how to do it exactly and while searching I came across postmessage WM_COPy and WM_Paste but don't how to implement. Still trying.

Vijay Yadav · Answer

ok that's good. Let see hope for the best.

Sam Hobbs · Answer

It is not an inconvenience. It is my body that keeps me awake longer than I want. It will be exciting to get it to work for you. I really hope that the time I have already spent will be beneficial for you.

Vijay Yadav · Answer

Thanks a lot Sam... I will go throuogh this and let you know. Please go to sleep as it is too late now. And Sorry for the inconvinience caused to you.

Sam Hobbs · Answer

I assume the Process class provides a way to start a process hidden. Please look to see if you can figure it out. The control ids are different for all the controls shown in that image. Assuming the controls are textboxes you need to use 3E8 3E9 and 3EF in the second parameter of the GetDlgItem function for each of the controls. Start Communication 3E8 Accept Bill 3E9 ? 3EF You will need to spend some time learning what the functions do. I will try to explain anything you need help with but you need to also read the documentation. When using the Windows API windows are identified by a window handle. Please look at the documentation of SendMessage; it is important that you understand how it works. The first parameter of SendMessage is the window handle. The second parameter is the message id. The other two parameters are the wparam and the lparam. The value of wparam and the lparam depends on what the message is. You can look up in the MSDN what each message is for example WM_GETTEXT message . The GetWindowThreadProcessId is used here to get the process id for a window handle. I use it here to ensure that I have the correct window handle for the Save As dialog. You might not need to do that in your program. The GetDlgItem function is used to determine the window handle of a control when we know what the control id is but we do not know what the handle is. FindWindowEx is used to find a window that matches a specified criteria. Here I use it to find the Save As dialog box. You might not need to do that in your program. I can understand that programmers not experienced with Windows programming using the Windows API would be confused by the Windows API. It is nearly 5 PM for you in India but it is after 3 AM for me. I need to get to sleep soon.

Vijay Yadav · Answer

Property of that controls are attached in the file. Please find it.

Vijay Yadav · Answer

And it says 'TextBoxhWnd' does not exist in the current context.

Vijay Yadav · Answer

Hi Sam I am not getting you. I want to know how to call that applciation and hide it as i don't want to display that application.

Sam Hobbs · Answer

The following are the pieces for getting text from a window in another process: const int WM_GETTEXT = 0x000D; const int WM_GETTEXTLENGTH = 0x000E; [DllImport( user32.dll  CharSet = CharSet.Auto)] static extern IntPtr SendMessage(IntPtr hWnd int Msg int wParam StringBuilder lParam); int length = SendMessage(TextBoxhWnd WM_GETTEXTLENGTH 0 IntPtr.Zero).ToInt32(); StringBuilder sbtext = new StringBuilder(length); int hr = SendMessage(TextBoxhWnd WM_GETTEXT length sbtext).ToInt32();

Sam Hobbs · Answer

Can you post the properties of two or more of the buttons? I mean something like:

Vijay Yadav · Answer

I got the ID of the application through Spy++. Here it goes Window 000D0678 ID003 Basic Driver V1.6 #32770 000606B0 'START COMMUNICATION BUTTON' 000B079C 'ACCEPT BILL' 000606B2 'EDIT' As soon as the communication is established through serial port 'Edit' will get value and I need to copy this to my application and click the Accept Bill button without allowing this application to activate means it should be hidden. Vulpes and Sam I am trying to get this done soon as i don't have much time now. Please help me.

Vijay Yadav · Answer

Sam. Any idea?

Vijay Yadav · Answer

Hi Sam I went through the explanation of Spy++ now the thing is that the file which i sent you in that there is one panel and inside that there is four button and for all four button i get the same id or it is showing the Id of that panel. Can you please suggest?

Sam Hobbs · Answer

Oh and I wish you guys used zip files instead of rar files. Modern versions of Windows has support for zip files provided with it. I am not aware of any advantage of rar files.

Sam Hobbs · Answer

I knew you were going to ask that question. I did not explain that since I explained it in your Sending data from one application to another application file thread. So please go ahead and read what I said there. Note for me I had to use the x64 version of Spy++; the x86 version did not work with Notepad. You will find the 64-bit version in the same directory as the x86 version.

Vijay Yadav · Answer

Hi Sam Thanks for your reply. I want to know that how can we find the textbox id and button id in order to perform the operation as the application is already build by other company. I have attached the image file of that aplication please have a look. All I need to first the copy the data from 'Denomination' tetxbox which is readonly and then i need to press the 'Accept Bill' button and that value should get copied to my application.

Sam Hobbs · Answer

This web site is not working perfectly. I am attaching a zipped version of the code. This is the same code that I posted in my previous reply but it should be easier to use.

Sam Hobbs · Answer

The following is a console program that executes Notepad puts some text into it then does a save but then it clicks the cancel button instead of saving the data. I do not consider this to be production-quality in the sense that I would add more error checking at least. This is a sample; at least it shows that it is possible. Note that control id values such as in the TextBoxId CancelButtonId and FileMenuId are usually constant for every application so once you determine those values for the application you ned to do this for you can use those values in your program without a need to modify the ids unless the other program changes and the values it uses has changed. using System; using System.Runtime.InteropServices; using System.Threading; namespace _162053 { class Program { const string ProgramLocation = @\Windows\system32\notepad.exe ; const string DialogClass = #32770 ; // (Dialog) const int TextBoxId = 15; const int CancelButtonId = 2; const int WM_SETTEXT = 0x000C; const int WM_COMMAND = 0x0111; const int BN_CLICKED = 0; const int FileMenuId = 3; [ DllImport ( user32.dll  CharSet = CharSet .Auto SetLastError = true )] static extern int GetWindowThreadProcessId( IntPtr handle out int processId); [ DllImport ( user32.dll )] static extern IntPtr GetDlgItem( IntPtr hWnd int nIDDlgItem); [ DllImport ( user32.dll )] static extern IntPtr PostMessage( IntPtr hWnd int Msg int wParam IntPtr lParam); [ DllImport ( user32.dll )] static extern IntPtr SendMessage( IntPtr hWnd int Msg int wParam IntPtr lParam); // overloaded SendMessage for strings [ DllImport ( user32.dll  CharSet= CharSet .Auto)] static extern IntPtr SendMessage( IntPtr hWnd int Msg int wParam string lParam); [ DllImport ( user32.dll  SetLastError = true  CharSet = CharSet .Auto)] static extern IntPtr FindWindowEx( IntPtr parentHandle int childAfter string lclassName int windowTitle); static void Main( string [] args) { System.Diagnostics. Process OtherProcess = new System.Diagnostics. Process (); OtherProcess.StartInfo.FileName = ProgramLocation; OtherProcess.Start(); OtherProcess.WaitForInputIdle(); // get the TextBox IntPtr TextBoxhWnd = GetDlgItem(OtherProcess.MainWindowHandle TextBoxId); Console .WriteLine( Process id: { 0:X } ; Main window: { 1:X } ; TextBox { 2:X }   OtherProcess.Id OtherProcess.MainWindowHandle.ToInt32() TextBoxhWnd.ToInt32()); // put some text into the TextBox string text = some text ; SendMessage(TextBoxhWnd WM_SETTEXT 0 text); // do a save; we must use PostMessage since SendMessage // would not return until the dialog is closed PostMessage(OtherProcess.MainWindowHandle WM_COMMAND FileMenuId IntPtr .Zero); Thread .Sleep(100); IntPtr SaveDialoghWnd = FindSaveAs(OtherProcess.Id); if (SaveDialoghWnd == IntPtr .Zero) { Console .WriteLine( SaveAs dialog not found ); OtherProcess.CloseMainWindow(); return ; } Console .WriteLine( Press a key and then the Save As dialog will be canceled ); Console .ReadKey(); // cancel the save. A BN_CLICKED message is sent to the dialog. First the's // window handle is found. IntPtr CancelButtonhWnd = GetDlgItem(SaveDialoghWnd CancelButtonId); int wParam = (BN_CLICKED SendMessage(SaveDialoghWnd WM_COMMAND wParam CancelButtonhWnd); Console .WriteLine( Press a key and then Notepad and this program will close ); Console .ReadKey(); OtherProcess.CloseMainWindow(); } /// /// Find the Save As dialog. I't kno how reliable this is; this is /// just for demostration purposes. /// /// Process id of the other process /// Window handle for the Save As dialog private static IntPtr FindSaveAs( int pid) { IntPtr SaveDialoghWnd = FindWindowEx( IntPtr .Zero 0 DialogClass 0); if (SaveDialoghWnd == IntPtr .Zero) return IntPtr .Zero; int processId; GetWindowThreadProcessId(SaveDialoghWnd out processId); if (processId != pid) return IntPtr .Zero; return SaveDialoghWnd; } } }

Sam Hobbs · Answer

If you are going to use SendMessage it would be easier to send a WM_SETTEXT message and put the text into the textbox directly. You can use WM_GETTEXT to get the data in a control. It is easier because you do not need to be concerned about setting focus or activating the application or waiting. And remember you can click a button directly instead of sending an enter key to do that.

Vulpes · Answer

As sending keystrokes seemed to work OK when the other application was visible I'd start by trying the same thing again but using SendMessage to send the keystrokes to the hidden window. As you need to wait for text to be pasted to the clipboard before you can read it SendMessage would be more appropriate than PostMessage though its signature is the same: [DllImport(User32.Dll)] static extern bool SendMessage(IntPtr hWnd uint msg int wParam int lParam); The list of virtual-key codes is here: http://msdn.microsoft.com/en-us/library/windows/desktop/dd375731(v=vs.85).aspx So to send the enter key VK_RETURN you'd use 0x0D: const int VK_RETURN = 0x0D; SendMessage(hWnd 0x100 VK_RETURN 0);

Sam Hobbs · Answer

Note that it is not as if SendMessage is a last-resort. For these requirements I know of no disadvantage of using SendMessage instead of PostMessage. If the requirements were different then SendMessage has the disadvantage of holding up the program but for the purpose of sending keys and responding to that it is preferred and probably necessary for the sending application to wait for the slave application. Note that messages are not enough for controls that were created for 32-bit Windows. You say what? I mean that SendMessage and PostMessage will work for Edit controls (TextBoxes) and ListBoxes because they existed in 16-bit Windows. So it is possible to use controls in other processes because Windows still supports use of the controls that existed in 16-bit Windows in the same way that they were used. Other controls such as the ListView control cannot be controlled so easily. So it depends on the application whether messages will work. If it can work then it is what most experienced Windows developers would use. The next level of sophistication is system hooks. You can use C# to do a low-level keyboard hook that can be used for just the one process. The problem is that a keyboard hook is not enough so you will need to use a little C++ to use hooks. There is something even more technical than hooks; that is to inject code into the other process. That is something you (your company) needs to spend a lot of money just to use it in a commercial application. Well there might be more economical versions but it is not free and/or you need to be very experienced with Windows to do any of that.

Vijay Yadav · Answer

ok! I got you and I saw that link also. I need to copy the value from another application and paste it in my applicaitona and hit the enter the button of that application afetre copying. so how to do that?

Vulpes · Answer

If you're still trying to use SendKeys to send keystrokes then as I said earlier it won't work with a hidden window - it can only send keystrokes to the currently active window. Your only hope is to use PostMessage or if you need to wait for each keystroke to be processed SendMessage.

Vijay Yadav · Answer

Hi Vulpes I tried this but it doesn't perform the action on that application as the application gets hide it sends the 'enter key' to my application button.

Vulpes · Answer

To hide a window and redisplay it again you can use the API functions ShowWindow or (perhaps better here) ShowWindowAsync which has this signature when used from C#: [DllImport(user32.dll)] private static extern bool ShowWindowAsync(IntPtr hWnd int nCmdShow); // constants needed for nCmdShow private const int SW_HIDE = 0; private const int SW_SHOWNORMAL = 1; private const int SW_SHOWMINIMIZED = 2; private const int SW_SHOWMAXIMIZED = 3; For the hwnd parameter you can use the same handle as you did when calling the SetForegroundWindow function. For example: ShowWindowAsync(procs[0].MainWindowHandle SW_HIDE);

Vijay Yadav · Answer

Hi Vulpes I don't want to kill a process all I want is to just hide that application because as I am using timer after every 3 second the focus move to another application and vice versa. I want to know is there any other alternative so that I should not use timer. For example ATM machine Already there is one screen as soon as we swipe the ATM card the event gets fired automatically and it move to the next page i.e. the PIN page where we enter the PIN number. I want to do something like that. Any idea?

Sam Hobbs · Answer

Please don't kill a process as part of the normal design of software. Use kill as a last resort and assume you system will then be unstable. As indicated in my reply to the other thread I agree that using something such as PostMessage is better if it is possible hoever PostMessage is asynchronous. It is better to use SendMessage if possible. It can be critical to use the appropriate one.

Vulpes · Answer

Well SendKeys only works if the application which is receiving the keys is the active application. This is why we had to call SetForegroundWindow to force focus onto it. You could minimize hide or kill it after you've sent the keys if that's any help? If it's not then you might be able to use the API function PostMessage to send the keys as this works with windows which don't currently have the focus or are minimized. In fact we had an example of using this function recently in this thread: http://www.c-sharpcorner.com/Forums/Thread/161095/send-key-to-jump-to-file-winamp-window.aspx Basically you need to use a tool such as Spy++ to find the class names for the controls so you can get their handles and post messages to them.

Vijay Yadav · Answer

Vulpes Thanks a lot for your support and for posting here :) Now the question is I don't the that another application to get activate over my application when the serial port connnection gets established that second application( from where I'm copying the data to the label text of my application) gets activated and i don't to show that application to the user. Any idea?

Vulpes · Answer

I'm moving over to this thread from this one: http://www.c-sharpcorner.com/Forums/Thread/112138/sending-data-from-one-application-to-another-application-fi.aspx so we don't get locked out as the post count reaches 40 (or so) which I've seen happen on several occasions in the past. For the benefit of Pramod and anyone else reading this thread we currently have this code which is producing no error but the label is blank: string text = Clipboard.GetText(); this.BeginInvoke(new MethodInvoker(delegate() { label1.Text = text; Regex rex = new Regex(@\d+); Match mm = rex.Match(label10.Text); if (mm.Success) { label1.Text = $  + mm.Value; } })); So USA 20 is in the Clipboard and should therefore be in the text variable and (initially at least) in label1.Text. I'd check the value in the debugger or do a MessageBox.Show just after that line to make sure it is. So what then is in label10.Text?

Vijay Yadav · Answer

Hi Pramod thanks for reply. I have used this and it gives error Cross-thread operation not valid: Control 'label1' accessed from a thread other than the thread it was created on.

Pramod Kumar Nandagiri · Answer

try using system.windows.forms.sendkeys.sendwait(your key); i think this may work in timer control